South Carolina / Barnwell County
Score 25 · moderate · #23 of 46 in SC
Crawl space moisture in Barnwell County, SC
Barnwell County scores moderate: no single wet-soil signal dominates its mapped acres. Where a seasonal water table is reported — 90% of acres — it averages 3.8 ft below grade.
- 1Water table 3.8 ft
- 2Wet soils 19%
- 3Moisture score 25
- 4EPA radon zone 3
Reading the Barnwell County soil survey
The score of 25 combines four parts, each from the USDA survey: wet drainage classes contribute 26.4 points of 100 on their own scale, group D soils 14.8, a shallow water table 37.6, and flooding 8.7; the weights are on the methodology page. The dominant hydrologic group is A (48% of acres): high infiltration, low runoff (sands, gravels).
At 3.8 ft the seasonal water table is usually below a crawl-space floor, but the 90% of acres that report one are by definition the wettest parts of the county; on those lots, a wet spring can bring water close to the footings.
Barnwell County against the rest of South Carolina
Barnwell County ranks 23 of 46 South Carolina counties, level with the state median of 25. That places it in the middle range, nationally and for the state. Statewide, 34% of mapped soil is in the wet drainage classes; here it is 19%, below the state figure — the score here comes from flooding and ponding rather than drainage class alone. After well drained, the next most common class is moderately well drained at 21%.
Flooding. 8% of acres with a flooding class are rated frequent; 1.1% of acres with a flooding class are rated occasional. Flood-prone soils are a minority here, concentrated along streams; the score mostly reflects what happens between floods.
What it means for a crawl space here
In a moderate county the soil record is mixed rather than uniformly wet, so conditions vary from lot to lot. Where the lot drains, the model-code default — a vented crawl space with 1 sq ft of net vent per 150 sq ft of floor, or 1 per 1500 with a Class I vapor retarder on the ground — is a reasonable starting point; where the sections above point to a shallow water table or flood-prone soil on your lot, plan as for an elevated county. Either way, check the site first: grading that falls away from the foundation, gutters and downspouts that discharge well clear of it, and a ground cover over bare earth. A wet crawl space in a moderate county points to one of those first.
Radon. EPA radon zone 3. The zone is a county-level prediction; EPA says elevated levels occur in every zone and every home should be tested.
Near Barnwell County by score
All 46 South Carolina counties
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area SC665; drainage covers 100% of 235,510 mapped acres); EPA Map of Radon Zones, county table (June 2024 JSON); IRC R408.3 Unvented crawl space, as adopted in S.C. Code Regs. 8-1221 (LII). Checked 2026-10-23.